The present invention relates generally to methods and materials for treating humans suffering from meningococcemia by administration of bactericidal/permeability-increasing (BPI) protein products.
Meningococcemia is an infectious disease caused by Neisseria meningitidis (also known as meningococcus) in which the bacteria and their products are found in the systemic circulation. Its clinical course varies from a relatively mild process to a severe, fulminant infection of sudden onset and extremely rapid progression, with the time from first fever until death spanning as little as 12 hours. The latter, dramatic form of the disease occurs in about 10% of patients infected with N. meningitidis. Patients may present with normal mental status and symptoms only of fever and petechiae, but may rapidly experience hemodynamic collapse, loss of the airway, and coma, along with severe coagulopathy, intravascular thrombosis, and organ failure. Alternatively, in late stages of the disease, patients may be unconscious and unresponsive at the time of presentation.
The mortality rate for acute meningococcal disease has not changed significantly over the last few decades despite technological advances in antibiotics and intensive care facilities. One retrospective study found that the mortality rate from meningococcal infection had not changed significantly over 30 years, even after adjusting for disease severity Havens et al., Pediatr. Infect. Dis. J., 8:8-11 (1989)!. Another prospective study of meningococcal infections Powars et al., Clin. Infect. Dis., 17:254-261 (1993)! in the years 1986 through 1991 reported that 113 patients with bacteriologically proven N. meningitidis infection were observed, of whom 15 (13%) died. This mortality rate of 13% had not changed appreciably from the mortality rate of 16% reported five decades earlier in a Chilean epidemic.
An "epidemic" is defined as an increased frequency of disease due to a single bacterial clone spread through a population. Although epidemics of meningococcemia are widespread in the developing world, no national epidemic has occurred in the United States since the 1940's. However, a significant increase in the endemic occurrence of meningococcemia, along with localized epidemics has occurred in the mid-1990s. The disease continues to be seasonal, with peak incidence in the late winter and early spring. Between 60% and 90% of all cases occur in children, with the peak incidence in children under age 2.
N. meningitidis is an encapsulated gram-negative coccus, typically occurring in pairs (diplococci), which is responsible for a spectrum of severe diseases, including meningococcemia. Meningococci are divided into nine serogroups on the basis of their capsular polysaccharides, with serogroups A, B, C, Y, and W135 accounting for the majority of clinical disease. These serogroups are further subdivided into antigenically distinct serotypes on the basis of expression of outer membrane proteins. Specific clones within each serogroup can be further delineated by protein electrophoretic patterns. The outer membrane of meningococci also contains a form of lipopolyaccharide (LPS), i.e., "lipooligosaccharide" (LOS), which is a common component of the outer membrane of gram-negative bacteria.
The meningococcus is known to colonize the nasopharynx of 5-15% of individuals; however, only a small fraction of those colonized will experience invasive disease. The transition from colonization to invasive disease is multifactorial and incompletely understood. The presence of viral upper-respiratory infections, which also peak during the late winter and spring, may damage the nasopharyngeal epithelium and permit bacterial translocation across an altered barrier. In children under 2 years of age, inadequate development of antibodies directed against the meningococcal polysaccharide capsule is thought to account for the high attack rate in this population.
The spectrum of disease caused by the meningococcus includes meningitis, arthritis, pericarditis, endocarditis, conjunctivitis, endophthalmitis, respiratory tract infections, abdominal and pelvic infections, urethritis, and a chronic bacteremic syndrome. The predominant clinical syndromes requiring pediatric intensive care unit (PICU) admission are meningitis and meningococcemia (with or without meningitis). The clinical presentation depends on the compartment of the body in which the infection and its inflammatory sequelae are primarily localized.
In contrast to meningococcemia, meningitis is a disease in which the bacteria are localized to the meningeal compartment, with signs consistent with meningeal irritation. Clinically, meningococcal meningitis is dramatically different from meningococcemia, however, it may be indistinguishable from other forms of meningitis, and only differentiated by culture or immunologic assays. Systemic hemodynamic signs, severe coagulopathy and intravascular thrombosis are notably absent. If properly treated, mortality is rare and neurologic sequelae, including sensineural hearing loss, is uncommon. The approach to diagnosis and treatment of meningococcal meningitis is the same as with other forms of bacterial meningitis.
If patients are examined early in the course of their disease when only petechiae and mild constitutional symptoms are evident, the diagnosis of meningococcemia may be complicated by the number of diseases which present with fever and petechiae in children, including, for example, infections by enterovirus, rotavirus, respiratory syncytial virus, Haemophilus influenzae, or Streptococcus pneumoniae; streptococcal pharyngitis; Rocky Mountain spotted fever, Henoch-Schoenlein purpura; or malignancy. However, since the outcome of meningococcal disease is highly dependent on rapid diagnosis and institution of antibiotics, the suspicion of meningococcemia must be aggressively pursued and treatment instituted, particularly since H. influenza meningitis has markedly decreased in the United States due to use of the vaccine against the bacteria.
Like other gram negative infections, the pathogenesis of severe meningococcemia is initiated by the endotoxin on, associated with or released from the bacteria. This bacterial endotoxin activates the pro-inflammatory cytokine cascade. In severe meningococcemia, the levels of bacterial endotoxin detected in the circulation by the LAL assay have been documented to be as much as 50-100 fold greater than levels documented in other gram negative infections. The complement cascade is also activated by bacteria and their endotoxin in the systemic circulation, producing anaphylotoxins which may mediate early hypotension and capillary leak.
In studies thus far, plasma levels of endotoxin Brandtzaeg et al., J. Infec. Dis., 159:195-204 (1989)!, TNF Van Deuren et al., J. Infect. Dis., 172:433-439 (1995)!, IL-6 Van Deuren et al., supra!, and fibrinogen, as well as prothrombin time (PI) McManus et al., Citical Care Med., 21:706-711 (1993)! in meningococcemia patients have been correlated with the severity and outcome of disease, although the correlation is imprecise. It has been suggested that combining ranked values for endotoxin, TNF, IL-1 and IL-6 can achieve a score that accurately reflects patient outcome Bone, Critical Care Med., 22:S8-S11 (1994)!.
Severe coagulopathy and intravascular thrombosis may be rapidly progressive and lead to ischemic injury of extremities and vital organs in meningococcemia patients. Respiratory failure, renal failure, adrenal failure and coma may develop. Petechiae and purpura may be extensive and become confluent, in which case the term "purpura fulminans" has been applied. In meningococcemic patients with severe disease, significant reductions in the coagulation inhibitors antithrombin III, activated protein C, and protein S have also been documented. These reductions may reflect a relative imbalance of anti-coagulant factors compared to pro-coagulants, but may also reflect the general consumption of all classes of factors. Quantitative deficiencies may also reflect hemodilution and capillary leak of proteins.
Severe cardiac dysfunction is often present on admission, or may develop within the first 24 hours. Ejection fractions of 20% or less are frequent. Cardiac dysfunction may be secondary to a number of factors, including: 1) myocarditis, which is present to varying degrees in a majority of autopsy specimens; 2) myocardial depressant substances; 3) intravascular thrombosis and subsequent myocardial ischemia; 4) myocardial interstitial edema, resulting in a non-compliant ventricle; 5) hypoxic myocardial injury; and 6) metabolic abnormalities.
Hypotension and circulatory insufficiency are multifactorial, with significant contributions from intravascular volume depletion, capillary leak, profound vasodilation (secondary to anaphylotoxins, nitric oxide, histamine, and other mediators), and depressed myocardial performance. Organ damage secondary to hypotension, intravascular thrombosis, and direct inflammatory damage may be evident at presentation.
Fulminant disease may be associated with adrenal hemorrhage, adrenal cortical necrosis, and rapid demise (Waterhouse Friederickson Syndrome). Even extensive adrenal hemorrhages, however, do not necessarily denote adrenal insufficiency, since normal or even elevated systemic cortisol levels have been documented in such patients. In a minority of patients with rapidly progressive disease, adrenal hemorrhages are associated with serum cortisol levels which are normal or subnormal (in a setting where elevated levels are expected). Other metabolic derangements such as metabolic acidosis, hypoglycemia, hypocalcemia, and hypomagnesemia are also frequently present.
Patients with severe disease are at highest risk of mortality. If they survive, they often experience severe morbidities, including extensive tissue and bone destruction that requires debridement and/or amputation followed by skin grafting procedures. In one study Powars et al., supra!, among the 28 patients with purpura fulminans, the hallmark of severe meningococcemia, 14 patients (50%) died. Of the 14 surviving patients who had purpura fulminans, 10 suffered soft tissue gangrene with deforming autoamputation. In another report Genoff et al., Plastic Reconstructive Surg., 89:878-881 (1992)!, six patients with meningococcemia and purpura fulminans were followed, of whom four patients required severe amputations (wrist or above for the upper limbs, or ankle or above for the lower limbs). Genoff et al. note that even after the life-threatening acute phase of the disease has passed, complications continue and require revisions to a higher level of amputation and multiple grafting procedures. Sheridan et al., Burns, 22:53-56 (1996), confirms that meningococcemia with purpura fulminans has a reported mortality rate of 50%, with high rates of major amputations in survivors. In their experience, surviving patients are often left with full thickness wounds involving the skin, subcutaneous tissue and often underlying muscle and bone; half of the surviving patients require major amputations.
Patients with meningococcal disease may also develop neurologic sequelae, including electroencephalogram (EEG) abnormalities, computerized tomography (CT) scan abnormalities, hearing impairment and neuropsychological testing deficits. In one study, 99 consecutive children and adult patients with acute, bacteriologically confirmed meningococcal disease were followed and tested for neurologic sequelae one year after their illness. Naess et al., Acta Neurol. Scand., 89:139-142 (1994).! In the category of patients suffering from meningococcemia with hypotension and/or ecchymoses, but without signs of meningitis, neurologic sequelae were observed in 5 of the 12 patients. In the category of patients suffering from meningococcemia with hypotension and/or ecchymoses, and with signs of meningitis, neurologic sequelae were observed in 7 of 13 patients.
Clinical outcome can be reasonably predicted by scoring of risk factors originally identified in large cohorts of meningococcemia patients. In 1966, Stiehm and Damrosh, J. Pediatrics, 68:457-467 (1966), reviewed 63 cases of meningococcal infection and identified clinical features associated with poor outcome. Poor prognostic factors included: onset of petechiae within 12 hours prior to admission, absence of meningitis (cerebrospinal fluid (CSF) WBC &lt;20), shock (systolic blood pressure&lt;70), normal or low white blood count (WBC &lt;10,000), and normal or low erythrocyte sedimentation rate (&lt;10 mm/hr). The presence of 3 or more of these criteria was associated with poor outcome. Niklasson et al., Scand. J. Infect. Dis., 3:17-25 (1971), substantiated these risk factors in 1971, and added temperature &gt;40.degree. C. and thrombocytopenia to the list of poor prognostic signs. The specific predictive abilities of the Stiehm and Damrosh criteria and the Niklasson criteria have been challenged in a series from McManus McManus et al., supra! in 1993. In this series, mortality was significantly less than predicted by earlier criteria and was more likely related to the presence or absence of coagulopathy.
The most widely used meningococcal sepsis scoring system was published in 1987 by Sinclair et al., Lancet, 2:38 (1987), and has become known as the Glasgow Meningococcal Septicemia Prognostic Score (Glasgow score). Its utility stems from its reliance on bedside clinical indicators, which facilitates triage in the field or during transport. Points are given on a rated scale for seven parameters as follows: (1) BP &lt;75 mm Hg systolic, age &lt;4 years or BP &lt;85 mm Hg systolic, age &gt;4 years (3 points); (2) skin/rectal temperature difference &gt;3.degree. C. (3 points); (3) modified coma scale &lt;8, or deterioration of 3 or more points in 1 hour (3 points); (4) deterioration in hour before scoring (2 points); (5) absence of meningism (2 points); (6) extending purpura or widespread ecchymoses (1 point); and (7) base deficit (capillary or arterial) &gt;8 (1 point). The maximum Glasgow score is therefore 15 points.
Since meningococcemia is frequently characterized by rapid and fulminant deterioration, vigilant monitoring is mandated. The great majority of patients should be admitted directly to the intensive care unit, where invasive monitoring can be instituted, and supportive therapy provided. Specific additions to monitoring and laboratory evaluation may include obtaining samples from CSF, blood cultures, skin lesions and throat swabs. However, CSF should be obtained only if the patient's clinical condition is stable enough to tolerate the procedure. Blood cultures should be obtained, but are positive in only 50% of untreated patients. Bacteria can also be detected in up to 70% of cases by Gram stain and culture of aspirated (or biopsied) hemorrhagic skin lesions. Examination of skin lesions is especially important for cases in which antibiotics have been administered prior to obtaining blood cultures. Throat swabs, if carefully obtained and rapidly plated, may also yield meningococci and support a presumptive diagnosis of meningococcemia. Alternatively, CSF may be obtained for detection of meningococcal antigens. If an organism is obtained, it should be serotyped and forwarded to a reference laboratory for additional subtyping. Epidemic control through immunization can only occur if the specific organisms responsible for disease are identified. In the unusual circumstance in which blood cultures cannot be obtained, antibiotics should still be administered without delay; microbiologic investigation can be accomplished at a later time by alternate methods.
Management of children with meningococcemia relies on intensive, aggressive monitoring and therapy. In particular, early protection of the airway, aggressive volume replacement, and appropriate institution of vasoactive agents, e.g., epinephrine, dopamine and dobutamine, are critical to restore tissue perfusion and oxygen delivery. A few specific issues in the treatment of meningococcemia, including treatment with antibiotics, steroids, fresh frozen plasma (FFP) replacement, heparin, and several new agents are briefly highlighted below.
An ongoing debate continues concerning whether antibiotics should be administered as soon as the diagnosis is suspected or after a period of stabilization. Although not resolved by randomized trials, the preponderance of evidence suggests that antibiotics should be administered immediately, while other supportive therapies are being instituted. Speculations regarding a post-antibiotic release of bacterial endotoxin in meningococcemia have not been substantiated by human data. Serial quantitation of bacterial endotoxin levels in plasma samples from humans with meningococcemia have failed to demonstrate a post-antibiotic surge in plasma endotoxin levels.
Initial therapy of suspected cases currently is typically recommended to be a third generation cephalosporin (e.g. Ceftriaxone) until other causes of severe infectious purpura with shock have been ruled out (H. influenza, S. pneumoniae, other gram negative bacteria). Therapy can then be switched to parenteral penicillin or ampicillin.
To date, there are currently no randomized, placebo controlled data to support the routine use of corticosteroids in patients with meningococcemia. However, data have demonstrated that a minority of patients with severe disease and adrenal hemorrhage exhibit normal or subnormal levels of plasma cortisol (in a situation during which elevated levels are expected). Although the lack of data precludes an affirmative or negative recommendation, the physician should consider administering adrenal replacement steroids (hydrocortisone 1-2 mg/kg i.v.) in a clinical situation of rapidly progressive shock that is unresponsive to fluids and inotropes.
There have also been to date no randomized, placebo controlled data to determine whether, or to what degree, biochemical coagulopathy should be treated with FFP. Although correction of biochemical abnormalities may appear logical, administration of FFP has been viewed by many as "fueling the fire" of coagulopathy. In a case-control trial of 336 patients in Norway, treatment with plasma or blood products (as opposed to albumin or plasma substitutes) was independently associated with poorer outcome. A surge in plasma endotoxin was also documented in a C6 deficient human following FFP administration during treatment for meningococcemia. These data suggest that administration of FFP may be harmful in some situations and therefore should be done carefully and only when there are compelling clinical indications.
Although small retrospective reports advocate the use of heparin as a treatment for purpura fulminans, the preponderance of data (small randomized trials and large case-control studies) do not indicate a beneficial effect of heparin therapy. There is currently no evidence to support the routine use of heparin in the treatment of meningococcemia. A large scale, double-blind, placebo-controlled Phase III trial of a monoclonal anti-lipid A antibody (HA-1A) in meningococcemia has been conducted in Europe. No results have been published to date.
In addition, a number of other biological agents are candidates for treatment of severe coagulopathy and intravascular thrombosis. These agents include: antithrombin III, protein C, and tissue factor pathway inhibitor. Anecdotal experiences with protein C and antithrombin III have already been published pending definitive trials. Other clinical interventions have been reported but have not been systematically tested, including: plasma and whole blood exchange, leukaplasmapheresis, continuous caudal blockade to relieve lower extremity ischemia, and topical application of nitroglycerin to vasodilate the peripheral vascular bed.
BPI is a protein isolated from the granules of mammalian polymorphonuclear leukocytes (PMNs or neutrophils), which are blood cells essential in the defense against invading microorganisms. Human BPI protein has been isolated from PMNs by acid extraction combined with either ion exchange chromatography Elsbach, J. Biol. Chem., 254:11000 (1979)! or E. coli affinity chromatography Weiss, et al., Blood, 69:652 (1987)!. BPI obtained in such a manner is referred to herein as natural BPI and has been shown to have potent bactericidal activity against a broad spectrum of gram-negative bacteria. The molecular weight of human BPI is approximately 55,000 daltons (55 kD). The amino acid sequence of the entire human BPI protein and the nucleic acid sequence of DNA encoding the protein have been reported in FIG. 1 of Gray et al., J. Biol. Chem., 264:9505 (1989), incorporated herein by reference. The Gray et al. amino acid sequence is set out in SEQ ID NO: 1 hereto. U.S. Pat. No. 5,198,541 discloses recombinant genes encoding and methods for expression of BPI proteins, including BPI holoprotein and fragments of BPI.
BPI is a strongly cationic protein. The N-terminal half of BPI accounts for the high net positive charge; the C-terminal half of the molecule has a net charge of -3. Elsbach and Weiss (1981), supra.! A proteolytic N-terminal fragment of BPI having a molecular weight of about 25 kD possesses essentially all the anti-bacterial efficacy of the naturally-derived 55 kD human BPI holoprotein. Ooi et al., J. Bio. Chem., 262: 14891-14894 (1987)!. In contrast to the N-terminal portion, the C-terminal region of the isolated human BPI protein displays only slightly detectable anti-bacterial activity against gram-negative organisms. Ooi et al., J. Exp. Med., 174:649 (1991).! An N-terminal BPI fragment of approximately 23 kD, referred to as "rBPI.sub.23," has been produced by recombinant means and also retains anti-bacterial activity against gram-negative organisms. Gazzano-Santoro et al., Infect. Immun. 60:4754-4761 (1992).
The bactericidal effect of BPI has been reported to be highly specific to gram-negative species, e.g., in Elsbach and Weiss, Inflammation: Basic Principles and Clinical Correlates, eds. Gallin et al., Chapter 30, Raven Press, Ltd. (1992). The precise mechanism by which BPI kills gram-negative bacteria is not yet completely elucidated, but it is believed that BPI must first bind to the surface of the bacteria through electrostatic and hydrophobic interactions between the cationic BPI protein and negatively charged sites on LPS. In susceptible gram-negative bacteria, BPI binding is thought to disrupt LPS structure, leading to activation of bacterial enzymes that degrade phospholipids and peptidoglycans, altering the permeability of the cell's outer membrane, and initiating events that ultimately lead to cell death. Elsbach and Weiss (1992), supra!. LPS has been referred to as "endotoxin" because of the potent inflammatory response that it stimulates, i.e., the release of mediators by host inflammatory cells which may ultimately result in irreversible endotoxic shock. BPI binds to lipid A, reported to be the most toxic and most biologically active component of LPS.
BPI has never been used previously for the treatment of subjects infected with N. meningitidis, including subjects suffering from meningococcemia. In co-owned, co-pending U.S. application Ser. Nos. 08/378,228, filed Jan. 24, 1995, 08/291,112, filed Aug. 16, 1994, and 08/188,221, filed Jan. 24, 1994, incorporated herein by reference, the administration of BPI protein product to humans with endotoxin in circulation was described. See also, von der Mohlen et al., J. Infect. Dis. 172:144-151(1995); von der Mohlen et al., Blood 85:3437-3443 (1995); de Winter et al., J. Inflam. 45:193-206 (1995)!. Thornton et al., FASEB J., 8(4):A137, 1994, report that BPI inhibited the release of TNF in vitro by human inflammatory cells in response to LOS derived from two Neisseria species, N. meningitidis and N. gonorrhea; and the report in International Application Publication No. WO 94/25476 published Nov. 10, 1994, of methods of treating endotoxin-related disorders, including Gram-negative meningitis.
In spite of treatment with antibiotics and state-of-the-art medical intensive care therapy, the mortality and morbidities associated with human meningococcemia remain significant and unresolved by current therapies. New therapeutic methods are needed that could reduce or ameliorate the adverse events and improve the clinical outcome of human meningococcemia, including, for example, reducing mortality, amputations, grafting procedures, permanent neurologic impairment and improving pediatric outcome scores.